Classification and prevalences of plaque streptococci after two years oral use of chlorhexidine

The purpose of the present study was to examine the influence of two years daily oral use of chlorhexidine (Löe et al. 1976) on the distribution of different streptococcal types in dental plaque. Plaque samples were collected from the molars in 16 persons in the chlorhexi dine group and from 17 control persons having used placebo solution. The samples were homogenized in yeast extract, and dilutions plated on mitis salivarius agar incubated micro aerophilically for 24 hours followed by aerobic storage at room temperature for 24 hours.
Colonies of each morphological type present were counted on plates having 30–300 colonies and their number related to the total number. One colony of each type was isolated and identified by biochemical tests. The study showed that 84.8 % of the strains could be classified as S. mutans, S. sanguis, S. mitior, S. milleri, S. salivarius , a group intermediary to S. sanguis and S. mitior , and a group resembling S. milleri , using only five biochemical tests: production of extracellular polysaccharide from sucrose, fermentation of mannitol, raffinose and inulin, and hydrolysis of esculin. In the chlorhexidine group the prevalences of S. sanguis and the group of streptococci intermediary to S. sanguis and S. mitior were higher, and the prevalence of S. milleri plus streptococci resembling S. milleri lower, among the streptococcal flora in dental plaque than those observed in the control group.